Stratigraphy of the Washakie Formation in the Washakie Basin, Wyoming GEOLOGICAL SURVEY BULLETIN 1369 Stratigrap?y of the Washakie_. Form.ation· -in the W qshakie · Basin, Wyoming By HENRY W. ROEHLER GEOLOGICAL. SURVEY BULLETIN 1 3 6 9 The name Washakie F?rmation is revived for Eocene fluvial . rocks that overlie the Green River Formation in the Washakie Basin. The formation is then divided into the· Kinney Rim and Adobe Town Members UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1973 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 72-600329 For sale by the Superintendent of Documents, U. S. Government Printing Office t Washington, D. C. 20402 Stock No. 2401-00286 CONTENTS Page Abstract ------------------------------------------------------- 1 Int~~-9-tion ---:-----.---:------------------------------'--------- 1 ·!F>.'q:rpose of mvestigatiOns __ ----__ --____ --_ --____ ----_______ _ 1 Acknowledgments -----------------------------------------­ 2 Location and geologic setting of the Washakie Basin ----------­ 2 Nomenclature and history of geological and paleontological in- vestigations __________ --__ -------------------------------- 3 Gompa'risons of the Washakie, Bridger, and Uinta Formations _ 8 Washakie Formation __________________________________________ _ 12 Kinney Rim Member --------------------------------------­ 12 Adobe Town Member --------------------------------------- 14 Outcrops -------------------------------------------------- 16 Haystack Mountain ------------------------------------- 17 Adobe T·own ------~------------------------------------ 18 Eastern, northern, and southern Washakie Basin --------- HI Western Washakie Basin ------------------------------- 19 Source areas and mineralogy -------------------------------- 21 Correlations ----------------------------------------------- 22 Age and faunal relations -----------------------------------­ 23 Type Sections and principal reference sections ---------------- 26 References cited _ -----__________________________________ -------- 39 ILLUSTRATIONS Page PLATE 1. West-east stratigraphic section and electric log cross section of the Washakie Formation and adjacent parts of the Laney Shale Member of the Green River Formation and Cathedral Bluffs Tongue of the Wasatch Formation in the Washakie Basin, Wyo- ming ------------------------------____________ In pocket 2. Graphic sections of the Washakie Formation in the Washakie Basin, Wyoming ----------------------In pocket FIGURE 1. Map showing the major physiographic features of the Washakie Basin --------------------------------- 5 III IV CONTENTS Page FIGURE 2. Gorre·lation1 chart of the Green River, Washakie, and Uinta Formations ------------------------------- 11 3-10. Photographs of: 3. The white ridge marker bed (bed 515) on the east slopes of Kinney Rim ---------------- 14 4. The robin's-egg-blue marker bed (bed 579) -- 16 5. Outcrops of the Adobe Town Member at the east edge of Haystack Mountain ---------- 17 6. Outcrop·s of the Adobe Town Member at Adobe Town ------------------------------------ 18 7. Outcrops of the lower brown sandstones in Wild Rose Draw ------------------------- 19 8. The sandstone rim below the Adobe Town Rim ------------------------------------ 20 9. The arkosic sandstones of the Adobe Town Mem- ber that cap Haystack Mountain ---------- 20 10. De~ert p·avement in the western part of the Washakie Basin -------------------------- 21 TABLES \ Page TABLE 1. Lithologic ~ifferences between the · Kinney Rim and Adobe Town Members of the Washakie Formation __ 13 2. Vertebrate •localities and partial list of fauna in the Washakie~ Formation ----------------------------- 25 STRATIGRAPHY OF THE WASHAK.ffi FORMATION IN THE WASHAKIE BASIN, WYOMING By HENRY W. RoEHLER ABSTRACT Since 1869 fluvial rocks of middle _and late Eocene age in the Washakie Basin in southwest Wyoming have been variously assigned to the Bridger Formation, the undivided Bridge-r and Uinta Formations, or the Washakie Formation. In this report the name Washakie Formation is reintroduced for use in the Washakie Basin, and the names Bridger Formation- and Uinta Formation are dropped in that basin. The Washakie Formation is a thick sequence o.f interbedded tuffaceous and arkosic sandstone; gray, green, or red mudstone; and minor thin beds of tuff, lime,stone, conglomerate, shale, and siltstone. The beds are numbered, described, and assigned to newly named members for which type sections and principal reference sections are designated, and key reference horizons ar·e shown in correlation diagrams. The lower 900± fe·et of the formation is named the Kinney Rim Member; the upper 2,300± feet of the formation is named the Adobe To.wn Member. The two members are separated by an unconformity, and are distinguished by minor lithologic diffe·rences. The Kinney Rim M·ember is missing in the eastern part of the basin, partly by erosion and truncation and partly by complex intertonguing and lateral re­ placement by the Laney Shale Member of the Green River Formation. The members are ·exposed in badlands between major sandstone ridges that slope basinward toward the central-southwestern part, or structural center, of the Washakie Basin. The Adobe '!'own Member_ comprises the youngest Tertiary strata across the center of the basin. - Vertebrate fossils are widely distributed, and they indicate a middle Eocene (Bridger A-B and Bridg·er C-D) age for the Kinney Rim Member and a middle Eocene (Bridger C-D) and late -Eocene (Uinta B) age· for the Adobe Town Member. The age and stratigraphic relations of the Bridger, Washakie, and Uinta Formations are briefly reviewed. INTRODUCTION PURPOSE OF INVESTIGATIONS Geologic mapping and stratigraphic studies by the U.S. Geo­ logical Survey to locate and evaluate oil-shale deposits in the intermontane Tertiary basins of the Central Rocky Mountains 1, 2 STRATIGRAPHY, WASHAKIE FORMATION, WASHAKIE BASIN have included investigation of Eocene rocks in the Washakie Basin in southwest Wyoming where thick oil-shale deposits are known. In 1968 a field reconnaissance was made in this poorly explored desert basin, numerous stratigraphic s·ections were meas­ ured, and a geologic map was prepared at the scale of 1 : 125,000 on a planimetric base. From this reconnaissance work, a strati­ graphic framework of key beds and unit contracts was developed for the geologic mapping of nearly fifty 71f2-minute quadrangles that cover the Washakie Basin. The purpose of this paper is to describe briefly the fluvial rocks of middle and late Eocene age that overlie the Green River Formation in the remote central part of the basin, to define the major stratigraphic units, and to review information bearing on their ages. Certain changes and refinements in the stratigraphic nomenclature are also proposed. The name Washakie Formation is revived for rocks formerly assigned to the undivided Bridger and Uinta Formations, or the Bridger Formation, and the names Kinney Rim and Adobe Town are proposed as members of the Washakie Formation. ACKNOWLEDGMENTS I thank C. L. Gazin, of the National Museum of Natural History, and P. 0. McGrew, of the University of Wyoming, for identify­ ing vertebrate fossils and establishing their ages. The generous aid of W. D. Turnbull, of the Field Museum of Natural History, who has accompanied me on numerous long field trips through the basin to ·establish stratigraphic correlations, and who has allowed the publication herein of new faunal data from his re­ cent collections, is appreciatively acknowledged. W. J. Mapel, G. E. Lewis, W. C. Culbertson, W. D. Turnbull, P. 0. McGrew, J. D. Love, and D. N. Miller, Jr., read the manuscript and sug­ gested changes. LOCATION AND GEOLOGIC SETTING OF THE WASHAKIE BASIN The Washakie Basin is a structural and topographic basin which consists of an area of aJbout 2,500 square miles north of the Colorado-Wyoming State line in southwest Wyoming (fig. 1). The basin is bounded by the major structural features, the Sierra Madre and the Rock Springs uplift to the east and west respec­ tively, and by the minor anticlinal folds, the Wamsutter Arch and the Cherokee Ridge to the north and south respectively. The overall configuration of the basin is that of a very broad, roughly square bowl having an encircling rim formed by the Laney Shale Member of the Green River Formation. Along its western part the rim is known as Kinney Rim, and in its northern part it is INTRODUCTION 8 known as Laney Rim. The asymmetri-cal shape of the basin results from the presence of several anticlinal noses that plunge basin..: ward from the basin margins. The major synclinal axis is ori­ ented in a northeast direction, slightly west of the geographic center of the basin. Lacustrine and fluvial Eocene rocks nearly 8,000 feet thick are exposed in badlands and ridges aeross the basin, except in small areas where the later Tertiary Bishop Conglomerate and Browns Park Formation cap high ridges, and where Quaternary alluvium and sand dunes fill intermittent stream valleys and cover areas of low relief. Major topographic features formed lby outcrops of the Washakie Formation, such as Adobe Town and Haystack Mountain, are discussed in detail later in this report. Altitudes above sea level range from 8, 700 feet at Pine Butte in the western part of the basin to 6,100 feet in drainages in the southeastern part of the basin, and they average about 6, 700 feet. Rainfall is less than 10 inches per year, which supports